Maike Currie, investment director for personal investing at Fidelity, said: “It can be easy to leave things to the last minute and your Isa allowance is no exception. It is issued on a ‘use it or lose it’ basis so if you miss the deadline you have lost it for good.”

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The good news is you get another allowance from April 6, which is also worth £15,240, rising to £20,000 in April 2017.

Currie says there are strong arguments for using your allowance at the start of each tax year as it gives your money a full 12 months of taxefficient growth.

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Fund manager Fidelity International says March 30 was the No 1 day for Isa investing

It can be easy to leave things to the last minute and your Isa allowance is no exception

Maike Currie

If you had invested £1,200 in the FTSE All Share at the end of each tax year for the past 10 years, you would have £13,664 today, but if you had invested at the start of each year instead, you would have £1,534 more at £15,198.

Alternatively, set up a monthly savings plan and that way you need not worry about markets crashing after investing a large lump sum.